The band feeding and tightening process performed by means of the aforenoted type of strapping machine is divided into the following processes: the band is fed toward the outside of the main body and positioned around the article to be strapped by means of a band guiding arch, or alternatively, manually, a leading end of the band is grasped by means of a press member and then the band is wound around the article to be strapped by means of a band-restoring and tightening mechanism disposed within the main body so as to define a primary tightening operation, and finally tightened so as to closely bind the strap around the article to be strapped and thereby define a secondary tightening operation. If the processes are subdivided, a series of the band feeding and tightening operations are performed as band-feeding, primary tightening, and secondary tightening operations, and the strength of the band tightening force around the article to be strapped can be adjusted depending upon the kind of article to be strapped.
The applicant has proposed a band-tightening apparatus, disclosed in Japanese U.M. Laid Open Publication No. 129703/1986 and illustrated in FIGS. 2 to 4, comprising a feed motor 21 provided with a speed reducer 22 attached to a base plate 41, a feed roller 23 driven by directly connecting the same to the feed motor 21, a shaft support plate 88 provided with an upper roller 24 mounted upon the base plate 41 and rotating in contact with the feed roller 23, a freely pivotable feed cover 75 disposed downstream of both rollers as viewed in the band-passing direction of both rollers, and a band chute 74.
As illustrated in FIGS. 2 to 4, the upper roller 24 is supported upon a shaft passing through a shaft supporting plate 88 which also includes an annular projection 83 upon which a bearing 29 is mounted. In other words, the shaft support plate 88 is mounted upon the right side of the feed roller 23 so as to cover a stepped portion 66 formed upon the base plate 41, as viewed in FIG. 4. A shaft 25 is mounted upon the shaft support plate 88 through means of the bearing 29 and an eccentric shaft 26 formed integrally with the front end of the shaft 25 is provided so as to project through the shaft support plate 88 as best seen in FIG. 3(B). The eccentric shaft 26 faces the space defined to the right upper of the feed roller 23 and above the stepped portion 66 formed upon the base plate 41 and the upper roller 24 is supported by means of the eccentric shaft 26. The front end of the shaft 25, namely the outer periphery of the portion projecting outwardly from the shaft support plate 88 is provided with a torsion spring 76, one end of which is secured to the shaft 25, and the other end of which is locked to the front end of a stopper pin 78. The rear end of the stopper pin 78 is capable of insertion into and removal from a plurality of adjusting holes 77 arranged concentrically with respect to the shaft 25 of the shaft support plate 88. Accordingly, the eccentric shaft 26 is biased in the counterclockwise direction as viewed in FIG. 3(A) by means of the torsion spring 76 and is caused to pivotally rotate roller 24 in the same direction as that of the biasing force of the eccentric shaft 26, so that the upper roller 24 is brought into compressive contact with the feed roller 23. The shaft 25 of the upper roller 24 is disposed above the driving shaft 37 of the feed roller 23 at an angle of approximately 15 degrees with respect to the horizontal plane. Accordingly, the band is held between both rollers in the form of a substantially reversed letter S, such that the frictional resistance of both rollers with the band is enhanced during the tightening operation. A cut-away portion 86 is formed within plate 88 by cutting the upper end margin of the shaft support plate 88 directed toward the feed roller 23 in the form of a triangle thereby enabling the pivotal rotation of the feed cover 75 as will be described later.
The feed cover 75 is composed of a finger-shaped rear end portion and a forward end portion having a stepped portion 67 formed upon one side thereof. The rotating space of the upper roller 24 is provided beneath the rear end portion of cover 75 and is situated within the vicinity of the upstream end of the band as viewed in the band-feeding direction and a shaft 81 provided with a torsion spring 79 of a relatively weak opposing strength is mounted within the upper portion of plate 88 so as to pivotably support cover 75. Accordingly, the feed cover 75 is mounted between the shaft support plate 88 and the base plate 41 by means of the shaft 81 for enabling free pivotal rotation thereof. The front end portion of the feed cover 75 is thick enough to cover the feed roller 23 and the finger portion is disposed above the upper surface of the stepped portion 66 of the base plate 41. The lower surface of the front end portion of the feed cover 75 is provided with a stepped portion 67 which opposes the circumferential surface of the feed roller 23 through the intermediary of a gap sufficient enough for allowing rotation of the roller 23 and which also opposes the forward surface of the stepped portion 66, as viewed in the band-feeding direction, formed on the base plate 41 through the intermediary of a gap for allowing the band to pass therethrough, with the thickness of the gaps of course corresponding to the thickness of or greater than that of the band. The front end margin or the side surface of the thick portion of the feed cover 75 is disposed substantially flush with the side margin of the base plate 41. The torsion spring 79 biases the shaft 81 in the counterclockwise direction with respect to FIG. 3(A), so that the front end portion of the feed cover 75 is normally biased in the direction toward the feed roller 23 by means of its own weight.
A series of band passages 80 is defined between the stepped portion 66 of the base plate 41 and the outer peripheral surface of the upper roller 24, between the outer peripheral surfaces of both rollers 23 and 24, and between the outer peripheral surface of the feed roller 23 and the lower stepped surface 67 of the feed cover 75, and the outlet of the band passage 80 faces the inlet of the band chute 74 and the inlet of the band passage 80 faces the outlet of a band-introducing pipe 33.
The feed roller 23 is connected to the motor 21 rotating normally at a constant speed and torque through the intermediary of the speed-reducing mechanism 22.
The rotary shaft in the speed-reducing mechanism and/or the driving shaft 37 of the feed roller 23 is provided with an electromagnetic clutch, a friction clutch and a one-way clutch. The rotation of the high-speed or low-speed output shaft is transmitted to the feed roller 23 through the intermediary of a chain, a pulley and other movement transmission members. Means for varying the voltage applied to the electromagnetic clutch performs band-feeding and primary tightening at high speed and low torque and secondary tightening at low speed and high torque.
In the above-described band-feeding and tightening apparatus, the band introduced into the main body is then fed into the band chute 74 through the intermediary of the band-introducing pipe 33 and the series of the band passages 80 and through the band-passing hole of the right press 54 to the outside of the main body. A predetermined amount of the band fed to the outside of the main body is manually stretched upon an article to be strapped and disposed upon an upper surface table (not shown), and then the front end of the band is inserted into a band-inserting portion 82 so as to perform a series of tightening, fusing and cutting operations thereon, and then band feeding within the final process is performed for a period set by means of a timer. If an external force which interferes with the advance of the feeding band, such as, for example, friction between the band and the respective mechanisms, is encountered during the band feeding, the band may be folded bent out of shape in the form of a superimposed waveform below a slide table 18 having wide spaces formed upon the upper and lower surfaces thereof and within the band chute 74, resulting in a so-called jam having a zig-zag form or a similar jam within the band passage 80. In such a case, a very complex operation is required such as, for example, the removal of the support plate 88 from the base plate 41 so as to permit the removal of the jammed band from the portion thereof and the cutting of the band at the jammed portions thereof which cannot be re-used because the band at the jammed portions has undergone plastic deformation, such that a most serious situation may be developed from the standpoint of the operation of the strapping machine. The above situation frequently occurs when a flexible, narrow and soft plastic band is used.
However, in the above-described prior art, the feed cover 75 is pivotably mounted, under the influence of its own weight, by means of shaft 81 provided with the torsion spring 79 of a relatively weak opposing force and is merely slightly biased in the direction toward the feed roller 23, so that an external force raises to some degree the front end portion of the feed cover 75 through means of the band. The band which is loosened to a degree corresponding to the raised distance of the cover 75 is retained between the stepped portion 66 of the base plate 41 and the stepped portion 67 provided upon the front end portion of the feed cover 75. In such a way, the external force is momentarily released and the band is smoothly fed to the outside of the main body by means of both, continuously rotating rollers.
In the aforenoted Japanese U.M. Laid Open Publication No. 129703/1986, the rear end finger portion of the feed cover 75 is pivotably supported so as to release the front end portion of the feed cover 75. For this reason, an article to be strapped is nearly always situated upon the upper portion of the feed cover 75 having the aforenoted construction, so that the feed cover 75, which contacts the bottom surface of the article to be strapped and which is hence not opened to a large extent, can resolve small jam problems but cannot resolve large jam problems.
In addition, even if the pivotable fulcrum is transferred to a position which is defined at a more rear and lower location with respect to the side of the upper roller 24 and the feed cover 75 is prevented to contact the bottom surface portion of the article to be strapped so that the feed cover 75 can be opened to a great extent and so that the band can be fed to the outside of the main body so as to free the band in the form of a ring, the ring portion of the band is sent out toward the bottom surface of the article to be strapped upon the upper portion thereof and eventually strikes the bottom surface thereof, whereby the band has its escape cut off and a jam is produced. Although the article to be strapped may be instantly transferred, of course, from the upper table after completion of the strapping operation, removal of the article to be strapped, which has completed the strapping operation, from the upper table is difficult from the standpoint of operability when a jam is produced with respect to the band. For this reason, the ring-like band which comes out when the feed cover 75 is opened strikes the bottom portion of the article to be strapped, thereby producing a jam as in the case with conventional examples. Because the feed roller 23 rotates so as to discharge the band irrespective of the force impressed upon the band which hinders the movement of the band when the band is fed, the band has its escape cut off so as to produce a jam below the slide table 18, within the band chute 74 or within the band passage 80. In the worst situation, the band may be caught between the stepped portion 66, of a circular notch 71 provided in series with the stepped portion 66 formed upon the base plate 41, and the feed roller 23.
In such a case, therefore, the jammed portion of the band should be cut because it cannot be reset for use due to plastic deformation thereof and the band must be pulled with a large amount of strength in order to resolve the worst jam in which the band may be caught between the notch 71 and the feed roller 23, so that there is a serious problem in operational efficiency from the standpoint of waste of the band material.
All conventional strapping machines as well as the above-described conventional means have used three-phase or single phase induction motors for providing versatility in accordance with the power sources of three-phase alternating current distributed to factories and the like (200 V) or general domestic single phase alternating current power sources (100 V), whereby the induction motor is rotated at a predetermined speed of rotation, in the area and the rotational force is transmitted to a feed roller through means of a speed-reducing mechanism and a friction clutch. Although such induction motors comprise common drive means, conventional strapping machines have used AC motors using the above friction clutches, electromagnetic clutches and various types of movement transmission mechanisms by only emphasizing manufacturing inexpensive strapping machines without the use of parts such as, for example, A/C transformation devices and rectifiers. Consequently, the above-described prior art must indispensably use friction clutches, one-way clutches and various types of movement transmission mechanisms. Accordingly there are problems encompassing a large number of parts, complex assembling processes and large-sized apparatus.
In order to obtain high torque during the secondary tightening operation, the rotational speed of the motor is reduced by means of a speed reducing mechanism and the feed roller is merely subjected to forward and reverse rotation at a predetermined low speed of rotation. For this reason, the band-feeding is slow and the band-tightening force is weak regardless of however strong the compressive force of the upper roller 24 on the feed roller 23 is made. Although the strapping machine is suited for strapping a relatively small special article to be strapped and is used as a table strapping machine, usages such as, for example, the motor being directly connected to apparatus installed upon an automatic strapping line, and the strapping of wood, wooden boxes and relatively large carton boxes has involved some difficulty.